One day Chad posed the question: how high can you count with stamps? 32? 55? The next day, Dennis began buying old stamps of various values and sticking them on a piece of plexiglass, realizing that the sum of 1, 2, 3, ..., 24 equals the postage for priority mail (we usually send our plexiglass priority). Isn't it wonderful when things just work out perfectly? Well, almost perfectly: he tried to create the sequence out of a single series... can you tell which one? Do you know which of these stamps don't belong? Click here to see an enlargemed detail of this piece.